Evaluation of Aortic Hemodynamics and Compliance in Aortic Stenosis

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Project Summary Bicuspid aortic valve (BAV) is the most common congenital heart defect, and it predisposes patients to complications such as aortic stenosis (AS, most common cause) and aortic aneurysm. Current metrics are ineffective at distinguishing patients with BAV and TAV and concomitant AS, and management of AS in patients with BAV and trileaflet aortic valves (TAV) is nearly identical under current guidelines. Current clinical care involves ultrasound as well as CT or contrast enhanced MRI to generate angiograms, and surgical thresholds are based on diameters and growth rates in the ascending aorta. The goal of this project is to develop a high-resolution self-navigating bSSFP sequence and then combine it with 4D flow data in an automated pipeline to allow improved characterization of the anatomy and hemodynamics of the aorta. While 4D flow, a method pioneered in our lab, enables acquisition of temporally and spatially resolved 3D flow velocity without using contrast, the technique could be improved by incorporating higher-resolution scans with improved blood-tissue contrast. Delineation of the volume of the aorta in patients with AS from 4D flow data alone has also historically proven more challenging due to the presence of a high-speed flow jet. Clinical translation of 4D flow is also limited by a time-intensive analysis workflow, so this project includes both the sequence development aims as well as the goal of developing an automated cloud-based analysis pipeline for the data. Close collaboration with clinicians will ensure that calculated metrics are relevant and presented in a manner that could be useful in the clinical staging or management of these patients. The first aim of this proposal is development and validation of a balanced steady-state free-precession (bSSFP) sequence to collect improved anatomic data with high resolution and blood-tissue contrast to improve diameter measurements of the ascending aorta and enable segmentation of the aorta at several time points in the cardiac cycle. This will allow calculation of relative area change as a surrogate for aortic compliance and examination of the wall shear stress dynamics over the cardiac cycle. The second aim will incorporate this higher-resolution data and 4D flow data into a highly automated pipeline that will enable rapid segmentation of the aorta and calculation of the wall shear stress dynamics and relative area changes. In the third aim, 20 BAV and 20 TAV patients with AS will be recruited from the patient population at Northwestern, then imaged and analyzed using the new protocol. This will demonstrate the feasibility of using the method in a clinical setting, while also contributing to answering the question of if AS is a separate clinical entity in BAV and TAV patients. Clinical collaborators will help guide the project to fulfil the ultimate goal of improving clinical imaging and staging of these complex patients.